Lyme borreliosis is the most common vector-borne infection in the United States [S. W. Barthold, et al., "An Animal Model For Lyme Arthritis", Ann. N.Y. Acad. Sci., 539, pp. 264-73 (1988)]. It has been reported in every continent except Antarctica. The clinical hallmark of Lyme Disease is an early expanding skin lesion known as erythema migrans (ECM), which may be followed weeks to months later by neurologic, cardiac, and joint abnormalities.
The causative agent of Lyme disease is a spirochete known as Borrelia burgdorferi, transmitted primarily by ixodes ticks that are part of the Ixodes ricinus complex. B. burgdorferi has also been shown to be carried in other species of ticks and in mosquitoes and deer flies, but it appears that only ticks of the I. ricinus complex are able to transmit the disease to humans.
Lyme disease generally occurs in three stages. Stage one involves localized skin lesions (ECM) from which the spirochete is cultured more readily than at any other time during infection [B. W. Berger et al., "Isolation And Characterization Of The Lyme Disease Spirochete From The Skin Of Patients With Erythema Chronicum Migrans", J. Am. Acad. Dermatol., 3, pp. 444-49 (1985)]. Flu-like or meningitis-like symptoms are common at this time. Stage two occurs within days or weeks, and involves spread of the spirochete through the patient's blood or lymph to many different sites in the body including the brain and joints. Varied symptoms of this disseminated infection occur in the skin, nervous system, and musculoskeletal system, although they are typically intermittent. Stage three, or late infection, is defined as persistent infection, and can be severely disabling. Chronic arthritis, and syndromes of the central and peripheral nervous system appear during this stage, as a result of the ongoing infection and perhaps a resulting auto-immune disease [R. Martin et al., "Borrelia burgdorferi--Specific And Autoreactive T-Cell Lines From Cerebrospinal Fluid In Lyme Radiculomyelitis", Ann Neurol., 24, pp 509-16 (1988)].
The neurologic manifestations of Lyme disease are protean and include weakness, peripheral nerve palsy, radiculitis, meningitis and encephalitis. The pathogenesis of neuroborreliosis, however, is unclear. Examination of the cerebrospinal fluid (CSF) of patients with neuroborreliosis shows a mononuclear pleocytosis and production of B. burgdorferi specific antibody, suggesting that inflammation is involved in disease. In some cases, spirochetes have been cultured from the CSF of patients with neurologic symptoms, implicating the organism directly with disease. Experiments using mice suggest that spirochete virulence may play a role in the development of neurologic infection.
Infection with B. burgdorferi induces a strong humoral immune response. Early in human infection, antibodies are generated primarily against the 41-kDa flagellar protein. In later stages, antibodies to the outer surface proteins OspA and OspB, among others, appear [J. E. Craft et al., "Antigens Of Borrelia burgdorferi Recognized During Lyme Disease", J. Clin. Invest., 78, pp. 934-39 (1986)].
Antibodies to the B. burgdorferi flagellin antigen remain prominent in patient serum during infection, and local CSF antibody production to spirochetal antigens, including flagellin, occurs. Further, the sera from patients with neurologic manifestations of Lyme disease have IgM antibodies that bind human axons; binding is weak or absent in patients without neurologic disease. The presence of high antibody titers in the CSF correlates with clinical signs of neuroborreliosis.
At present, all stages of Lyme disease are treated with antibiotics. Treatment of early disease is usually effective, however the cardiac, arthritic and nervous system disorders associated with the later stages often do not respond to therapy [A. C. Steere, "Lyme Disease", N. Engl. J. Med., 321, pp. 586-96 (1989)].
At present, Lyme disease is diagnosed primarily by serology. The enzyme-linked immunosorbent assay (ELISA) is one method of detection, using sonicated whole spirochetes as the antigen [J. E. Craft et al., "The Antibody Response In Lyme Disease: Evaluation Of Diagnostic Tests", J. Infect. Dis., 149, pp. 789-95 (1984)]. However, serologic testing is not yet standardized, and results may vary between laboratories and commercial kits, causing false negative and, more commonly, false positive results [S. Luger and E. Kraus, "Serologic Tests For Lyme Disease: Interlaboratory Variability," Arch. Int. Med., 150, pp. 761-63 (1990)]. In addition, available serologic tests have limited usefulness early in infection prior to the development of a measurable antibody response [R. Grodzickiano and A. C. Steere, "Comparison Of Immunoblotting And Enzyme Linked Immunosorbent Assay Using Different Antigen Preparations For Diagnosing Early Lyme Disease," J. Inf. Dis., 157, pp. 790-97 (1988)].
Because the B. burgdorferi flagellar antigen is detectable early in infection, it could potentially prove useful in a diagnostic test. However, the flagellar protein is known to contain epitopes which are conserved among other spirochetes [J. L. Coleman and J. L. Benach, "Identification And Characterization Of An Endoflagellar Antigen Of Borrelia burgdorferi", J. Clin. Invest., 84, pp. 322-330 (1989)], and the flagellin cross-reacts with antibodies directed against other bacterial flagellins [L. A. Magnarelli et al., "Cross-Reactivity Of Nonspecific Treponemal Antibody In Serologic Tests For Lyme Disease", J. Clin. Microbiol., 28, pp. 1276-1279 (1990)]. As a result, antibodies to this protein do not provide a specific marker for Lyme disease.
In view of the above, there exists an urgent need for a highly specific and sensitive laboratory test for detection of B. burgdorferi infection and diagnosis of Lyme disease. There also exists a need for therapeutic agents and methods of diagnosis and treatment that are useful in later stages of Lyme disease.